Redundant backlight for electronic display

Abstract

A first and second plurality of lighting elements are each capable of producing a desired overall luminance output for a backlight at power level P. A respective controller is in communication with each of the plurality of lighting elements. At least one of the controllers is configured to determine a threshold luminance output, measure a measured luminance output, apply a non-zero power level less than P to the plurality of lighting elements, and, when the measured luminance output drops below the threshold luminance output, increase the power level applied to at least one of the plurality of lighting elements, up to as high as power level P, to return the measured luminance output to said threshold luminance output.

What is claimed is: 
     
       1. A system for driving a redundant backlight at a desired overall luminance output comprising:
 a first and second plurality of lighting elements positioned to illuminate an electronic display, wherein the first and second plurality of lighting elements are each capable of producing the desired overall luminance output for the backlight at full power; 
 a first controller in communication with the first plurality of lighting elements; 
 a second controller in communication with the second plurality of lighting elements; and 
 software instructions, which when executed, configure at least one of the first and second controllers to:
 determine a threshold luminance output; 
 measure a measured luminance output; 
 operate the backlight in a first mode whereby the power level applied to each of the first plurality of lighting elements is substantially half power and the power level applied to each of the second plurality of lighting elements is substantially half power, until the measured luminance output drops below the threshold luminance output; and 
 automatically configure the backlight to operate in a second mode when the measured luminance output drops below the threshold luminance output, whereby in said second mode the power level applied to only one of said first plurality of lighting elements and said second plurality of lighting elements is increased sufficiently, up to as high as full power, to return the measured luminance output to at least said threshold luminance output, and no power is applied to the remaining plurality of lighting elements. 
 
 
     
     
       2. The system of  claim 1  wherein:
 said first plurality of lighting elements comprise light emitting diodes (LEDs); 
 said second plurality of lighting elements comprise LEDs; and 
 the electronic display is a liquid crystal type display. 
 
     
     
       3. The system of  claim 1  wherein:
 said first and second plurality of lighting elements are arranged to provide direct backlighting to the electronic display. 
 
     
     
       4. The system of  claim 1  wherein:
 said first and second plurality of lighting elements are arranged to provide edge lighting to the electronic display. 
 
     
     
       5. The system of  claim 1  wherein:
 the first plurality of lighting elements are positioned in a direct-lit arrangement and the second plurality of lighting elements are positioned in an edge-lit arrangement. 
 
     
     
       6. The system of  claim 1  wherein:
 the measured luminance output comprises data representing the current drawn by at least one of the first and second plurality of lighting elements. 
 
     
     
       7. The system of  claim 1  wherein:
 the measured luminance output comprises data representing the illuminance level provided by at least one of the first and second plurality of lighting elements. 
 
     
     
       8. The system of  claim 1  wherein:
 the first and second controllers are in a master/slave arrangement. 
 
     
     
       9. A system for driving a redundant backlight at a desired overall luminance output comprising:
 a first plurality of lighting elements positioned to illuminate an electronic display and capable of producing the desired overall luminance output for the backlight at power level P; 
 a second plurality of lighting elements positioned to illuminate the electronic display, wherein said second plurality of lighting elements are capable of producing the desired overall luminance output for the backlight at power level P; 
 a first controller in communication with the first plurality of lighting elements; 
 a second controller in communication with the second plurality of lighting elements; and 
 software instructions, which when executed, configure at least one of the first and second controllers to:
 determine a threshold luminance output; 
 measure a measured luminance output; 
 operate the backlight in a first mode whereby the power level applied to each of the first and second plurality of lighting elements is a non-zero value less than P; and 
 following detection of a failure in one of the first or second plurality of lighting elements, operate the backlight in a second mode whereby the power level applied to the remaining operable plurality of lighting elements is increased sufficiently, up to as high as said power level P, to return the measured luminance output to at least said threshold luminance output, and the failed plurality of lighting elements is turned off; 
 
 wherein the power level P is substantially full power; 
 wherein the non-zero value less than P is substantially one-half P; 
 wherein the non-zero value less than P applied to the first plurality of lighting elements is the same as the non-zero value less than P applied to the second plurality of lighting elements; 
 wherein said failure is detected when the measured luminance output drops below the threshold luminance output. 
 
     
     
       10. The system of  claim 9  further comprising:
 a first current source in electrical connection with the first controller and the first plurality of lighting elements; and 
 a second current source in electrical connection with the second controller and the second plurality of lighting elements. 
 
     
     
       11. The system of  claim 10  wherein:
 said failure is detected when the current draw from one of the first and second current sources drops to substantially zero. 
 
     
     
       12. The system of  claim 8  wherein:
 the first and second plurality of lighting elements are in an edge-lit arrangement. 
 
     
     
       13. The system of  claim 8  wherein:
 the first and second plurality of lighting elements are in a direct-lit arrangement. 
 
     
     
       14. The system of  claim 8  wherein:
 said first and second plurality of lighting elements are each comprised of light emitting diodes; and 
 the electronic display is a liquid crystal display. 
 
     
     
       15. A system for driving a redundant backlight for a liquid crystal display (LCD) at a desired overall luminance output comprising:
 a LCD stack; 
 a backlight placed behind the LCD stack and comprising:
 a first plurality of LEDs positioned in a direct-lit arrangement; and 
 a second plurality of LEDs positioned in an edge-lit arrangement; 
 wherein the first and second plurality of LEDs are each capable of producing a desired overall luminance output for the backlight when full power is applied to the respective plurality of LEDs; 
 
 a first controller in electrical communication with the first plurality of LEDs; and 
 a second controller in electrical communication with the second plurality of LEDs; 
 wherein the first and second controllers are configured to operate the backlight in a first mode whereby the power level applied to each of the first and second plurality of LEDs is substantially half power, until a time when a measured luminance output drops below a predetermined threshold luminance output; 
 wherein the first and second controllers are configured to automatically begin operating in a second mode when the measured luminance output drops below said predetermined threshold luminance output, whereby in said second mode the power level to only one of said first or second plurality of LEDs is increased sufficiently, up to as high as full power, to return the display to at least said predetermined threshold luminance output, and no power is supplied to the remaining plurality of LEDs.